The present invention relates to a structure material and a molded product using the structure material and a decomposing method for such a molded product. More specifically, the present invention relates to a structure material which has excellent mechanical strength and heat resistance and is easily decomposed at the time of disposal and a molded product using such structure material, and a decomposing method thereof.
In recent years, global environmental issues have been greatly paid attention to. In particular, regarding resin waste, it is desired: (1) to collect and recycle valuable substances from waste in order to avoid depletion of resources; and (2) to reduce the volume of waste to deal with a reduced space for burying refuse. However, the reduction in volume of the resin waste has hardly been promoted, and the resin waste is generally treated by burning.
Regarding a resin molded product, a molded product obtained by integrally molding a structure material together with at least a metal (e.g., a molded product such as a molded motor and molded transformer; a recording medium such as a magnetic tape, a magnetic disc and an opto-magnetic disc) are utilized in consumer equipment, industrial equipment, office equipment or the like. Taking a molded motor as an example, the demand for molded motors has rapidly expanded because of their excellent properties in terms of noise, damping, insulation and maintenance, and teir compact size facilitates automation thereof.
Conventionally, a molded stator of a molded motor used as an alternate current motor, a brushless direct current motor or the like generally has a structure disclosed in Japanese Laid-Open Patent Publication No. 61-214740. The structure will be described with reference to FIGS. 5 and 6. FIG. 5 is a perspective view showing an external appearance of a molded motor having a conventional molded stator 201. FIG. 6 is a perspective view showing the structure of a stator section before being molded. As shown in FIG. 5, the molded motor has a motor section 220 and a molded stator 201 which is integrally molded so as to cover the stator section of FIG. 6 with a molding compound 202. As shown in FIG. 6, the stator section has an iron core 204 wound by a wire 203 via a cylindrical insulator 207. The insulator 207 has a printed board 211 having a wiring pattern 210 at a part of its circumference at one end thereof. The terminal portion of the wire and a lead line 212 are connected on the printed board 211, and an external signal is input to the coil. The molding compound contains a thermoplastic resin such as polyethylene terephthalate, polyethylene, polypropylene and nylon, or a thermosetting resin such as an unsaturated polyester resin, a vinylester resin and a phenol resin as a binder, and further contains calcium carbonate, talc, carbon black or the like as an additive.
It is desirable at the time of disposal of the molded motor to remove the molding compound and recycle metals such as the iron core and the wires which are valuable. In conventional waste treatment, generally, the molding compound is crushed by a shredder at first, and then valuable substances such as the iron core and the wire are recovered from the debris for recycle. However, in such a structure of the molded motor, the iron core and the wire easily cause damage to the teeth of the shredder. Therefore, such a crushing treatment is not favored, and the valuable substances are disposed of without being recycled and then buried in the earth with other waste. Since the aforementioned molding compound is not naturally decomposed while being buried, a silicon steel plate or a copper wire used in the iron core and the wire are left in the land without being recycled, in spite of their high value as an after use material. In addition, since the reduction in volume of the molding compound has not been promoted, it becomes difficult to ensure space for burying it.
In the case where the molding compound contains a thermoplastic resin such as polyethylene terephthalate as the main component, polyethylene terephthalate can be dissolved in a mixing solvent of chlorophenol or metacresol and tetrachloroethane. Therefore, it is theoretically possible to remove such a molding compound by dissolving it in the solvent. However, the dissolution in the solvent takes an extremely long time. Moreover, such a mixing solvent is so toxic that the use thereof is restricted. In addition, in view of recent environmental issues, the use of such a solvent is out of the question. Therefore, in the conventional molded motor, the molding compound cannot be crushed, decomposed, dissolved nor reduced in volume, and thus poses the problem that it is difficult to recycle valuable substances such as the iron core and the wire at the time of disposal.
Regarding the molded product obtained by molding a structure material and a metal, other molded products such as a molded transformer and a magnetic tape have the same problems as the molded motor as described above.
As described above, in view of the decomposition and the reduction in volume of resin waste and recycle of valuable substances, a structure material which is readily decomposed while maintaining excellent characteristics of conventional structure materials is desired.
A structure material of the present invention comprises 20 parts by weight or more of a polymer mixture of a thermoplastic aromatic polyester and a thermoplastic aliphatic polyester on the basis of 100 parts by weight of the structure material. The content of the thermoplastic aromatic polyester in the polymer mixture is larger than the content of the thermoplastic aliphatic polyester.
In one preferred embodiment, the polymer mixture can be decomposed into a monomer unit by a decomposing solution containing a base and a hydrophilic solvent.
In one preferred embodiment, the mixture comprises 3 to 40 parts by weight of the aliphatic polyester on the basis of 100 parts by weight of the mixture.
In one preferred embodiment, the aliphatic polyester is at least one selected from the group consisting of polycaprolactone, polycaprolactone diol, polycaprolactone triol, polyethylene succinate, polybutylene succinate and polylactic acid.
The molded product of the present invention is formed of the structure material described above.
In one preferred embodiment, the molded product of the present invention is a recording medium including a substrate formed of the structure material and a recording layer provided on the substrate.
In one preferred embodiment, the molded product of the present invention is selected from the group consisting of a magnetic tape, a magnetic disc, an opto-magnetic disc and a phase change type optical disc.
In one preferred embodiment, the molded product of the present invention is formed by molding the structure material together with at least a metal.
In one preferred embodiment, the molded product of the present invention is a molded motor having a molded section formed of the structure material integrally molded containing the metal. The structure material contains an inorganic filler.
In one preferred embodiment, the molded section includes an internal molded section covering the metal and an external molded section which is provided outside the internal molded section and whose outermost portion defines an outermost portion of the molded product. The internal molded section is formed of the structure material. The external molded section is formed of a molding compound containing a thermosetting resin.
In one preferred embodiment, the molded product of the present invention is a molded motor having a molded section formed of the structure material integrally molded containing the metal and an insulator. A part of the insulator penetrates the molded section and is exposed flush with the surface of the molded section.
In one preferred embodiment, the molded section is formed of a molding compound containing a thermosetting resin. The insulator comprises 20 parts by weight or more of a polymer mixture of a thermoplastic aromatic polyester and a thermoplastic aliphatic polyester on the basis of 100 parts by weight of the insulator. The aliphatic polyester is at least one selected from the group consisting of polycaprolactone, polycaprolactone diol, polycaprolactone triol, polyethylene succinate, polybutylene succinate and polylactic acid.
A decomposing method for a structure material of the present invention includes the step of immersing the structure material in a decomposing solution containing a base and a hydrophilic solvent at a temperature lower than the boiling point of the hydrophilic solvent. The structure material comprises 20 parts by weight or more of a mixture of a thermoplastic aromatic polyester and a thermoplastic aliphatic polyester on the basis of 100 parts by weight of the structure material, and the content of the thermoplastic aromatic polyester in the mixture is larger than the content of the thermoplastic aliphatic polyester.
A decomposing method for a molded product of the present invention is a decomposing method for a molded product formed by molding a structure material together with at least a metal. The structure material comprises 20 parts by weight or more of a mixture of a thermoplastic aromatic polyester and a thermoplastic aliphatic polyester on the basis of 100 parts by weight of the structure material, and the content of the thermoplastic aromatic polyester in the mixture is larger than the content of the thermoplastic aliphatic polyester. The method includes the steps of immersing the molded product in a decomposing solution containing a base and a hydrophilic solvent at a temperature lower than the boiling point of the hydrophilic solvent, and decomposing at least a part of the structure material forming the molded product and then separating and collecting the metal.
In one preferred embodiment, the hydrophilic solvent is a mixed solvent of water and lower alcohol.
In one preferred embodiment, the separation and the collection of the metal are performed in a state where the structure material remains moist.